Organometallic compounds containing rhodium have been widely used as intermediates and catalysts. An outstanding example is "Wilkinson's Catalyst", [(C.sub.6 H.sub.5).sub.3 P].sub.3 RhCl, wherein (C.sub.6 H.sub.5).sub.3 P is triphenylphosphine [see G. W. Parshall, "Homogenous Catalysis", John Wiley & Sons, New York, NY, 8 (1980)]. It is perhaps the most versatile organic rhodium catalyst known. It has a square planar structure with the three (C.sub.6 H.sub.5).sub.3 P ligands and one chloride ligand in an array about a central rhodium atom: ##STR1## It is known in the art that "Wilkinson's Catalyst" undergoes equilibrium dissociation to produce [(C.sub.6 H.sub.5).sub.3 P].sub.2 RhCl, a highly reactive, three-coordinate, 14-electron intermediate, and one uncoordinated triphenylphosphine ligand. The dissociation reaction is as follows: EQU [(C.sub.6 H.sub.5).sub.3 P].sub.3 RhCl.revreaction.(C.sub.6 H.sub.5).sub.3 P+[(C.sub.6 H.sub.5).sub.3 P].sub.2 RhCl
The structural features of the intermediate contribute to high chemical reactivity in two ways: (1) Rh(I) normally is four coordinate and thus the "vacant" site in a three coordinate compound provides a binding site for a substrate molecule which will subsequently undergo a catalytic transformation; and (2) Rh(I) normally has 16 electrons in its outer shell, consequently, species with a 14 electron configuration will react rapidly with electron donor compounds such as alkenes, alkynes, carbon monoxide, nitric oxide and other compounds that will provide the needed extra electrons.
The prior art teaches the preparation and use of tris(triarylphosphine)rhodium(I) complexes having an anion coordinated to the central rhodium atom. A. Yamamoto, S. Kitazuma and S. Ikeda in J. Am. Chem. Soc. 90, 1089 (1968) disclose [(C.sub.6 H.sub.5).sub.3 P].sub.4 RhH and report that 0.4 mole of hydrogen per mole of Rh is liberated on acidolysis; the acid used is not disclosed and the product(s) of the reaction other than hydrogen are not isolated or characterized. Furthermore, no uses for the products are taught. K. C. Dewhirst et al. in Inorg. Chem. 7, 546 (1968), employ phenol as a proton source and note that its reaction with [(C.sub.6 H.sub.5).sub.3 P].sub.n RhH, wherein n is 3 or 4, produces [(C.sub.6 H.sub.5).sub.3 P].sub.n-1 RhOC.sub.6 H.sub.5. Again, the conjugate base of the acid remains bonded to the metal.
Yared et al., J. Am. Chem. Soc. 99, 7076 (1977) disclose certain rhodium perchlorate salts, i.e., [(C.sub.6 H.sub.5).sub.3 P].sub.3 Rh.sup.+ ClO.sub.4.sup.- and [(C.sub.6 H.sub.5).sub.3 P].sub.3 Rh(CO).sub.2.sup.+ ClO.sub.4.sup.-. Perchlorate salts of cations containing organic groups are generally recognized to be explosive.
U.S. Pat. No. 3,794,671 discloses a method of making Rh(I) compounds of the type [(C.sub.6 H.sub.5).sub.3 P].sub.3 Rh.sup.+ (anion).sup.-, where the anion is fluoroborate (BF.sub.4.sup.-), acetate, trifluoromethanesulfonate (CF.sub.3 SO.sub.3.sup.-), trifluoroacetate, or benzoate. These compounds are useful as catalysts in organic reactions such as hydrogenation, isomerization, and hydroformylation of olefins. In col. 3, lines 69-71, the patentee suggests that an ionic species is not present in [(C.sub.6 H.sub.5).sub.3 P].sub.3 Rh.sup.+ BF.sub.4.sup.- and that coordination to the BF.sub.4.sup.- ion exists. U.S. Pat. No. 3,794,671 also discloses certain rhodium carboxylates having the formula [(C.sub.6 H.sub.5).sub.3 P].sub.3 Rh(OCOR), wherein R is substituted or unsubstituted alkyl or aryl, and [(C.sub.6 H.sub.5).sub.3 P].sub.3 Rh(CO)BF.sub.4, the latter having been prepared by reaction of [(C.sub.6 H.sub.5).sub.3 ]P.sub.3 RhBF.sub.4 and CO.
R. R. Schrock et al., J. Am. Chem. Soc. 93, 2397 (1971) disclose various rhodium coordination compounds including [(C.sub.6 H.sub.5).sub.3 P].sub.3 Rh(CO).sup.+ ClO.sub.4.sup.- and [(C.sub.6 H.sub.5).sub.3 P].sub.3 Rh(CO).sub.2.sup.+ B(C.sub.6 H.sub.5).sub.4.sup.-. In this publication, the routes (solution phase) to cationic rhodium carbonyl compounds employ as starting materials cationic olefin complexes of rhodium.